In the sale and distribution of liquified petroleum fuel gas (L.P. Gas) to individual customers it is conventional for a distributor to use stationary, above ground bulk storage tanks, as large as sixty thousand gallons, to store the highly volatile and inflammable liquid under substantial vapor gauge pressure and then distribute it to customers by delivery truck tanks that are filled repeatedly from the storage tanks with the use of liquid flow and vapor return conduits that include flexible hoses detachably connected to the truck delivery tank. These conduits are permanently connected to the bulk storage tanks and have automatic cut off flow control valves between the storage tank and the hoses, and shut off valves at the free ends of the hoses connectible to truck tanks which in turn have safety flow check valves protecting it. The present invention is concerned with an excess vapor pressure equalizing return flow valve usable at either or both ends of the flexible hose.
By way of illustrating the extensive usefulness of this valve it is desirable that the conduits include quite flexible hoses to accommodate a random and quick positioning of a tank truck for rapid connection thereto and filling. Preferably the transfer hoses are short, approximately ten feet long (3 meters), and are comparatively small 1 1/4" and 2" (32 mm and 52 mm) in diameter for strength and ease of handling of vapor and liquid respectively, and also for rapid filling while, for safety, minimizing the volume of liquified gas present at any given time in the hoses between the tanks. The liquified gas in its liquid state may be forced by pump to flow or be permitted to flow under the influence of gravity through the liquid filler hose, with vapor pressures being equallized between the tanks by vapor return flow to minimize tank filling time and maximize customer deliveries.
Aside from maintaining the handling and filling equipment in acceptably safe condition, and in addition to dangers of fire and faulty equipment, an ever present random danger conventionally exists in which, for any one of several reasons, a delivery truck driver receiving L.P. Gas will occasionally move his truck during filling, or drive his replenished truck away while the hoses are still connected between the truck tank and storage tank. This can rupture either or both the hoses under substantial tension and gas pressure forces, and generally after such a hose rupture, there is substantial pressurized spillage of liquefied gas that rapidly creates a highly dangerous fire hazard before, and regardless of, the automatic closing of safety flow-check valves after a break. Substantial amounts of vaporized and expanding gas escape before conventionally arranged valves are effective. Automatic outflow cut-off transfer valves have been used such as described and claimed in application Ser. No. 708,128, where a trip cut-off cord is connected to the truck which trips a valve by unlatching a stop that supports a spring for closing a check valve in the outflow to the hose. Many times it has been found that the cord is not attached to the truck during filling operations.
However, if both hoses are ruptured, the escape of liquid provides a greater danger than escape from the vapor hose although already vaporized gas is one step closer to combining with air to provide an immediately combustible mixture which has explosive potential.
In the present invention, the valves are closed before a rupture occurs in either hose and at most any escaping gas would be only that in the filler hose. The check valve in the invention not only closes in the direction of outflow of vapor, it also closes the valve if a fire may already have been started from sparks or any one of several other reasons, thereby confining spillage to the short hose contents which if ignited would quickly burn out with minimal escape of gas with a fuse metal release also assuring automatic closing of a dispensing valve. These are improved safety steps.
One of the objects of the invention is to compel the followance of the proper sequence of the truck tank filling procedure in a way which automatically prevents any hazardous spillage if there is an inadvertant drive away without disconnection, and, prevents any further use without attention and repair.
Another object of the present invention is to enable quick preliminary equalization of vapor pressures between the two tanks for liquid transfer in that excess vapor flow closing sensitivity can be minimized if manually held but when unattended the sensitivity is automatically in effect.
Among the objects of the invention is the control and limiting of the escape of hazardous vapor to only a readily dispersible known amount and confine any damage to preventive equipment that is easily restored or replaced;
(a) to assure good inspection, testing and upkeep of frangible safeguards including hoses provided for the ultimate prevention of dangerous break-away spillage and fires;
(b) and safeguarding truck filling equipment against damage of any parts other than a replaceable preassembled hose unit rigidly supported against movement at its storage tank end.
The inertia force of flowing vapor in a conduit is less than that of liquid flowing in the same size conduit and to augment the prompt effectiveness of vapor it is preferred that the vapor conduit be appreciably smaller than the liquid conduit to assure a prompt vapor valve closure. Also in the connection preceding the closing of the valve the normal return movement of vapor to the bulk tank having minimal inertia can reverse its flow direction and accelerate quickly its effort for closing the vapor flow conduit at the valve.